The detection of metastatic breast cancer within the draining axillary lymph nodes of patients with primary breast cancer serves as an important prognostic indicator and provides a rationale for the administration of adjuvant chemotherapy. Currently, the assessment of nodal involvement is based upon a pathologist's histologic evaluation of a 6 micron section through each palpable lymph node. Hence, the accuracy of this crucial information is limited by (1) the inability of the pathologist to detect all lymphoid tissue within the fibroadipose tissue and (2) the sampling error inherent in examining only one histologic section from each node. Mathematical models have shown that the examination of a single lymph node section gives rise to a 30% probability of a false negative assessment. The validity of this concept has been borne out in studies where serial sections through lymph nodes results in the detection of "occult" metastases in 15-30% of cases which were "node negative" by conventional criteria. Therefore, we pose the question, "Can metastatic disease within the axilla more accurately or more easily be determined by an Eliza or a radioimmunoassay"?